The prior art of the present invention is hereinafter described with reference to the specification of Japanese Patent Application No. 264087/1984.
FIG. 25 is a partial perspective view of a heat-transfer unit according to one example of the prior art that is generally indicated by (1) and disposed in the direction of fluid flow A. The heat-transfer unit (1) is basically composed of heat-transfer fins, a heat generator, a heat absorber, a heat accumulator and a heat radiator. In FIG. 25, the heat-transfer unit consists of a plurality of heat-transfer elements (1a), (1b) and (1c), each being provided with a plurality of through-holes (13), which are stacked one on top another and the fluid flows through the passage formed by adjacent heat-transfer elements. Each heat-transfer element (1) is cyclically bent in the direction of fluid flow A in the form of trapezoidal waves, the bends in one element being out of phase with those in an adjacent element. The action of the mechanism of the heat-transfer unit shown in FIG. 25 is hereinafter explained with reference to FIG. 26 which is a cross-sectional view of the unit.
In FIG. 26, the fluid passage formed between heat-transfer elements (1a) and (1b) are indicated by (51), and the passage formed between (1b) and (1c) is denoted by (52). If it is assumed that the same volume of fluid flows in passages (51) and (52) under the same total pressure, the velocity of the fluid flowing in passage (51) through a cross section taken along the line X--X normal to the direction of fluid path A is smaller than the velocity of the fluid flowing in passage (52) through a smaller cross section that is also taken along the line X--X. Because of the resulting different that occurs between the static pressure in the passage (51) and that in the passage (52), part of the fluid will flow from the passage (51) into the passage (52) through-holes (13).
If one looks at the heat-transfer element (1b), the fluid will flow cyclically from the passage (51) to (52) and vice versa in accordance with the geometry of the generally trapezoidal waveform of the element, as shown in FIG. 2.
Therefore, if a heat-transfer unit is constructed in the manner described above in connection with an example of the prior art, surfaces where uniform fluid sucking occurs and those where uniform fluid-blowing occurs will be formed, one surface alternating with the other in the direction of fluid path. In the heat-transfer surfaces where uniform fluid-sucking occurs, very thin boundary layers will form to provide a remarkable improvement in heat-transfer, whereas in the surfaces where uniform fluid-blowing occurs, the repetition effect of promotion zones also contributes to high heat-transfer performance. These two effects combine together to promote heat-transfer to a dramatically high level that has theretofore been considered to be unattainable.
Furthermore, in the example shown above, the main stream of fluid A flows along each of the heat-transfer elements (1), producing only a small amount of branch stream that passes through-holes (13).
In other words, in one cycle of bends in each heat-transfer element (1), most of the fluid will flow along one surface of its passage and only a limited portion of the fluid will flow into an adjacent passage through-holes (13). As a result, the main stream of the fluid will flow undeflected along each heat-transfer element.
The same action of mechanism will occur in the next cycle of bends in each heat-transfer element.
With the heat-transfer unit described above, it is anticipated than an optimum configuration will exist for the heat-transfer elements because the heat-transfer characteristics of the unit will vary depending upon various shape parameters associated with the elements such as the ratio of passage (51) to adjacent passage (52) in terms of the area of cross section taken along the line X--X, the diameter of through-hole (13), their relative opening, and the periodicity of cyclic trapezoidal bends.